Autism is a disorder that has been first identified as “autistic disturbances of affective contact” by Dr. Kanner in U.S.A. in 1943. Onset of autism appears in an extremely early stage (before turning about three years old), and it includes, as principal symptoms, severe and sustained impairment in social interaction, deviance in communication, and patterns of behavior and interest that are restricted or stereotyped. Autism is a developmental disorder in which the condition changes in the course of development, and it is assumed to be a yet unspecified high-level central nervous system disorder.
High-functioning autism means autism, which does not have mental retardation. With regard to autism morbidity, it has been reported that 7 to 16 out of 10,000 children suffer from autism, and that high-functioning autism is about 11% to 34% of the autism (Macintosh et al., Journal of Child Psychology and Psychiatry 2004).
The cause of autism has not been clarified at present, and thus, the radical treatment method for autism has not been developed yet. Accordingly, educational intervention by experts (which is referred to as “intensive intervention”) based on early detection is important for the adaptation to social life of autistic patients. The earlier the time of initiation of such intensive intervention, the more effective it becomes. It is desired to begin such intervention before or after a child is two years old, at which the autistic symptoms appear for the first time. However, since objective and biological criteria for autism have not been established yet, doctor must diagnose autism only based on symptoms. For such diagnosis, abundant experience at the site of child psychiatry is required. Thus, under the circumstances in which there is a shortage of experts in this field, it is extremely difficult to detect an autistic patient at an early stage.
At present, the diagnosis of autism is made by conducting an interview with subjects using the diagnostic criteria of the American Psychiatric Association (DSM-IV), ICD-10 of World Health Organization (WHO), and ADI-R (Autism Diagnostic Interview-Revised).
Although the cause of autism has not been clarified yet, various reports have been made so far. For example, enlarged head circumference is observed at an early stage after the birth of an autistic child, and thus, it is considered that an increase in neurogenesis and/or gliogenesis or a decrease in cell death during this period is associated with the development of autism (McCaffery et al., Progress in Neurobiology 2005). Other than this report, Fatemi et al. have focused on developmental disorders of the central nerve system found in Reeler mice, and have reported that an increase in the mRNA level of a very low-density lipoprotein receptor (VLDL receptor) that is a receptor of the responsible gene Reelin of the Reeler mouse is found in the frontal lobe and cerebellum of an autistic patient after death (Fatemi et al., 2005). On the other hand, Sharp et al. have made a proteome analysis, and as a result, they have found a decrease in the concentration of apolipoprotein B-100 specific to autistic children (Corbett et al., 2007). Basically, VLDL is a complex of protein and lipid containing the apolipoprotein B-100, and a change in the expression of this molecule in vivo is anticipated to be associated with lipid metabolism. However, to date, there have been no reports of the lipid fractions of peripheral blood of autistic patients. Also, there have been no reports stating the relationship between autistic patients and serum lipid levels.
In addition, there has been disclosed an invention relating to the diagnosis of autism by measuring the amounts of specific growth factors in a serum sample (Japanese Patent Laid-Open No. 2008-32447). However, the behavior of these growth factors is never associated with lipid metabolism.
As described above, taking into consideration the specificity of the pathologic condition of autism, studies have been conducted directed towards establishing a comprehensive treatment system including prevention of this disorder based on early diagnosis, early treatment, and support of patients for social rehabilitation. However, a biological marker for autism, which enables early diagnosis, has not been developed yet.